Method of controlling the power input to a HVDC transmission link

1. A method of controlling the power input to a high-voltage direct-current (HVDC) transmission link, the HVDC transmission link is connected to an alternating-current (AC) power plant via a first voltage source converter and to an AC grid via a second voltage source converter, the method comprising:

performing voltage control of the HVDC transmission link during a no-fault mode of operation of the grid via the second voltage source converter;

monitoring a HVDC transmission link parameter to detect an unbalanced fault;

regulating the output of the AC power plant via the first voltage source converter in the event of an unbalanced fault, which is on the basis of the monitored HVDC transmission link parameter; and

wherein the regulating the output of the AC power plant comprises providing unbalanced multi-phase voltage reference signals at a collector network of the AC power plant; and

wherein the unbalanced multi-phase AC voltage reference signals are comprised of three voltage signals of different magnitudes for the collector network of a three-phase AC power plant.

2. The method according to claim 1 ,

wherein the unbalanced fault is detected when the monitored HVDC transmission link parameter exceeds a predefined threshold value.

3. The method according to claim 1 ,

wherein the monitored HVDC transmission link parameter comprises a HVDC transmission link voltage.

4. A control module for controlling the power input to a high-voltage direct-current (HVDC) transmission link, the HVDC transmission link is connected to an AC power plant via a first voltage source converter and to a grid via a second voltage source converter, comprising:

a monitoring means for monitoring a HVDC transmission link parameter;

a detecting means for directly detecting an unbalanced fault on the basis of the monitored transmission link parameter;

a regulating means for regulating the output of the AC power plant according to the monitored HVDC transmission link parameter;

wherein the regulating means is realized to generate an unbalanced multi-phase AC voltage reference at a collector network of the AC power plant; and

wherein the unbalanced multi-phase AC voltage reference comprises three voltage signals of different magnitudes for the collector network of a three-phase AC power plant.

5. The control module according to claim 4 , comprising:

a computer program product for carrying out the method according to claim 1 , when the computer program product is loaded into a memory of a programmable device.

6. A voltage source converter for a power plant, comprising a control module according to any of claim 4 .

7. A power generation and transmission arrangement, comprising:

an AC power plant for generating AC power;

an AC grid for consuming the generated AC power;

a high-voltage direct-current (HVDC) transmission link for transmitting the generated power from the AC power plant to the AC grid;

a first voltage source converter for converting AC power into DC power, arranged between a collector network of the AC power plant and the HVDC transmission link;

a second voltage source converter for converting DC power into AC power, arranged between the HVDC transmission link and the AC grid; and

a control module according to claim 4 for controlling the power input to the HVDC transmission link.

8. The power generation and transmission arrangement according to claim 7 ,

wherein the AC power plant comprises a wind power plant.

9. The power generation and transmission arrangement according to claim 8 ,

wherein the wind power plant comprises a number of variable-speed wind turbines realized to provide a balanced multi-phase current independent of a voltage imbalance.